Theme 5-7-Severity-frequency-duration measures for urban water supply systems.

Abstract

Urban water supply authorities are required to supply water to their customers (both bulk water customers and small users) with a certain level of reliability. Various indicators have been used in the past to measure the reliability of supply to these customers and mostly they are related to water restrictions. They include supply reliability, severity of restrictions and duration of restrictions. These measures in the past have not addressed the issue of frequency of meeting or violating these measures, although it is understood that this additional information would help the water supply planners and customers (especially the large bulk water users) in planning and managing their water supply and demand. This issue was addressed in this paper by deriving severity-frequency-duration (SFD) curves for use in management of urban water supply systems. A methodology, which uses water supply system simulation and partial duration series analysis, was developed to derive the SFD curves. The methodology was applied to a hypothetical two-reservoir system supplying water to a demand centre with typical urban restriction and other operating rules. The results showed that it was possible to derive a consistent set of SFD curves, which provided information on frequency of restrictions with different durations and severities.